# 0.75 Gbit/s high-speed classical key distribution with mode-shift keying chaos synchronization of Fabry–Perot lasers

## TL;DR

A new method for high-speed secure key distribution using chaotic laser synchronization achieves 0.75 Gbit/s over long distances.

## Contribution

A novel high-speed key distribution scheme using mode-shift keying chaos synchronization in Fabry–Perot lasers is experimentally demonstrated.

## Key findings

- A 0.75-Gbit/s key distribution rate was achieved with a bit error rate of 3.8 × 10−3 over 160-km fiber.
- The entropy rate of the laser chaos was evaluated as 16 Gbit/s, indicating high potential for final key rates.
- The method improves key distribution speed by using control codes rather than laser transition response times.

## Abstract

High-speed physical key distribution is diligently pursued for secure communication. In this paper, we propose and experimentally demonstrate a scheme of high-speed key distribution using mode-shift keying chaos synchronization between two multi-longitudinal-mode Fabry–Perot lasers commonly driven by a super-luminescent diode. Legitimate users dynamically select one of the longitudinal modes according to private control codes to achieve mode-shift keying chaos synchronization. The two remote chaotic light waveforms are quantized to generate two raw random bit streams, and then those bits corresponding to chaos synchronization are sifted as shared keys by comparing the control codes. In this method, the transition time, i.e., the chaos synchronization recovery time is determined by the rising time of the control codes rather than the laser transition response time, so the key distribution rate is improved greatly. Our experiment achieved a 0.75-Gbit/s key distribution rate with a bit error rate of 3.8 × 10−3 over 160-km fiber transmission with dispersion compensation. The entropy rate of the laser chaos is evaluated as 16 Gbit/s, which determines the ultimate final key rate together with the key generation ratio. It is therefore believed that the method pays a way for Gbit/s physical key distribution.

Two parameter-matched Fabry-Perot lasers injected by a super-luminescent diode, after independent and random mode selection, emit chaotic lights with synchronization on-off keying. Shared keys are extracted from the synchronous waveforms.